Work another agent has claimed is withheld: you get who holds it, not
the answer. Ask them, or pick up something else. If you genuinely must
have it, call again with `override` set to your reason, which is
recorded in the journal against your name.

`on_behalf_of` names a teammate when the agent is working for one. They
see only the folders they were actually shared, and nothing else.

Set `claiming` when you are about to start work on this, rather than
just noting something. Other agents are then told you have it and knos
withholds it from them until you finish or half an hour passes. Writing
a plain fact claims nothing: a note everybody can read is the point.